Proposal of a second generation of quantum-gravity-motivated Lorentz-symmetry tests: sensitivity to effects suppressed quadratically by the Planck scale

TL;DR

This paper discusses new experimental approaches using cosmic-ray and neutrino observatories to test Lorentz symmetry violations suppressed quadratically by the Planck scale, which were previously considered untestable.

Contribution

It proposes the first experimental framework to detect quadratically suppressed Lorentz-symmetry violations using advanced cosmic-ray and neutrino observatories.

Findings

Cosmic-ray observatories can test quadratic Planck-scale effects.

Neutrino observatories offer complementary sensitivity.

Potential to observe quantum-spacetime effects previously deemed untestable.

Abstract

Over the last few years the study of possible Planck-scale departures from classical Lorentz symmetry has been one of the most active areas of quantum-gravity research. We now have a satisfactory description of the fate of Lorentz symmetry in the most popular noncommutative spacetimes and several studies have been devoted to the fate of Lorentz symmetry in loop quantum gravity. Remarkably there are planned experiments with enough sensitivity to reveal these quantum-spacetime effects, if their magnitude is only linearly suppressed by the Planck length. Unfortunately, in some quantum-gravity scenarios even the strongest quantum-spacetime effects are suppressed by at least two powers of the Planck length, and many authors have argued that it would be impossible to test these quadratically-suppressed effects. I here observe that advanced cosmic-ray observatories and neutrino observatories can provide the first elements of an experimental programme testing the possibility of departures from Lorentz symmetry that are quadratically Planck-length suppressed.